The front end structure of an automotive vehicle is designed to provide visual appeal to the vehicle owner while functioning as an energy absorbing structure during frontal and offset crashes. The size, shape and construction of the front end structure contribute to the ability of the front end structure to attenuate the crash pulse and restrict intrusions into the operator's cabin of the vehicle. It is important to design a front end structure to absorb crash energy through the frame components. To that extent, a significant amount of effort by vehicle engineers is devoted to designing the vehicle frame to crush in a controlled manner while absorbing a maximum amount of energy.
One of the goals in the design of vehicle frame structure is to provide better engagement and absorption of energy during a collision. The major components in absorbing energy in frontal as well as rear impacts are the rails. Furthermore, in a side collision if the vehicle has a softer front end it can help mitigate the injuries to occupants in both vehicles. If there is an apparatus to absorb more energy and prolong the time to crush the rails, the crash pulse and intrusion into the passenger compartment can be reduced significantly.
Vehicle frames typically include an upper rail and a generally vertically spaced lower rail. Preferably, the upper rail joins the lower rail, such as at the forwardmost portion of the vehicle frame, to define an integrally connected automotive frame structure. The structural joint connection between the vehicular upper and lower structural member is conventionally designed as a solid connection which provided good structural integrity in all directions. While the formation of the upper and lower rail members is preferably accomplished through hydroforming techniques which forms the upper and lower rails as tubular members, the upper and lower rails can be formed of any material or any construction technique, including stamped and roll formed vehicular body structures.
The package constraint for the placement and design of the front rail system can present a problem with respect to the energy management function of the front end. In automotive frame configurations in which the package constraint forces the rail to bend downwardly as the horn section approaches the bumper beam, which will allow the automotive frame to meet a 16-20 inch bumper height requirement, a front impact exerts an offset eccentricity between the center of gravity at the bumper and the center of gravity of the subframe attachment. This offset eccentricity can result in a substantial external applied bending at the center of gravity of the front rail section, which can be a large percentage of the bending capacity of the front rail section. Thus, this external applied bending takes away from the section capability to manage the normal buckling and folding stresses due to axial collapse of the horn section of the lower frame rail member. This eccentricity of the frame configuration can result in a premature downward bending of the horn section at the onset of any axial crash.
One approach to resolving this package and loading constraint problem is to reinforce the rearward half or third of the horn section rail length closest to subframe attachment, at lower side of the section where buckling stresses are highest, resulting in a corresponding increase in the bending capacity of the horn section. Typically, this reinforcement is provided in the form of a vertically oriented flange extending downwardly from the horn section. While this reinforcing flange solution does achieve the desired increase in bending capacity in the horn section of the lower frame rail member, the increased bending capacity penalizes the crushability of the horn section over which this solution is implemented. As a result, the horn section can only effectively crush along the forward half or so of the length of the horn section projecting forwardly of the lower frame rail attachment, thus substantially reducing the crash energy management capability of the automotive frame.
In U.S. Pat. No. 6,695,393, issued to Fadhel Aouadi, et al on Feb. 24, 2004, and assigned to Ford Global Technologies, LLC, the concept of a double cell extruded rail having a horizontal middle wall separating the beam into upper and lower cells is disclosed. This double cell frame rail absorbs kinetic energy from a crash to prevent intrusion into the passenger compartment. U.S. Pat. No. 6,811,212 granted to Tatsuo Kasuga on Nov. 2, 2004, teaches a similar front rail structure with a horizontal central wall separating the beam into upper and lower cells. U.S. Pat. No. 6,302,478, issued on Oct. 16, 2001, and U.S. Pat. No. 6,412,857 issued on Jul. 2, 2002, both being granted to Federico Jaekel, et al, disclose a vehicle space frame including hydroformed tubular members which form a joint by using a pair of spaced wall portions extending around the end of the hydroformed tubular members.
U.S. Pat. No. 6,938,948, granted to Troy Cornell on Sep. 6, 2005, discloses an energy absorbing front frame structure in which engine cradle side rails are attached to the vehicle front end and include a crushable jointure joined by a non-deformable intermediate structure. This configuration allows the vehicle frame to absorb crash energy during frontal impacts to improve passenger safety.
Accordingly, it would be desirable to provide a structural joint between the upper frame rail member and the lower frame rail member that would resist premature bending due to a downward angle imposed on the horn section, while permit a collapsing of the horn section of the lower front rail member along the entire length thereof to effectively manage crash energy loading.